Method for producing polyamide 6 of a low extract content, high viscosity stability and low remonomerization rate

ABSTRACT

The continuous process for producing polyamides by reacting at least one aminonitrile with water comprises the following steps: 
     (10) reacting at least one aminonitrile with water at a temperature of from 200 to 290° C. at a pressure of from 40 to 70 bar in a flow tube containing a Brönsted acid catalyst selected from a beta-zeolite, sheet-silicate or metal oxide catalyst in the form of a fixed bed, 
     (11) diabatically or adiabatically expanding the reaction mixture from step (1) into a first separation zone to a pressure of from 20 to 40 bar, the pressure being at least 10 bar lower than the pressure in step (1), and to a temperature within the range from 220 to 290° C. by flash evaporation and removal of ammonia, water and any aminonitrile monomer and oligomer, 
     (12) further reacting the reaction mixture from step (2) in the presence of water at a temperature of from 200 to 290° C. and a pressure of from 25 to 55 bar and in the presence or absence of a Brönsted acid catalyst selected from a beta-zeolite, sheet-silicate or metal oxide catalyst in the form of a fixed bed, 
     (13) diabatically or adiabatically expanding the reaction mixture from step (3) into a second separation zone to a pressure of from 0.01 to 20 bar, the pressure being at least 20 bar lower than the pressure in step (3), and to a temperature within the range from 220 to 290° C. by flash evaporation and removal of ammonia, water and any aminonitrile monomer and oligomer.

Nylon-6 is used for the manufacture of fiber, film and moldings. Thepolymers obtained by melt polymerization include a high level ofε-caprolactam and of low molecular weight reaction products (oligomer)because of the chemical equilibria. Since caprolactam oligomer andcaprolactam monomer are soluble and extractable in water, the level oflow molecular weight constituents in the polymer is also known as itsextractables content.

To prevent any impairment to product quality and processing properties,for example during injection or extrusion molding or during spinning,the extractables content has to be lowered.

The requisite extraction is usually carried out with water at elevatedtemperatures, as described for example in DE-A-25 01 348 or DE-A-27 32328. To increase the yield of the polymerization and to avoid anyadverse impact on the environment, aqueous extracts are frequently notdisposed of as waste, but are recycled.

The lower solubility of oligomer and especially dimer is not the leastreason why complicated and energy-intensive processing steps have to beused for the extraction in order that polyamides of satisfactory qualitymay be obtained. In existing processes, caprolactam monomer is used as asolubilizer for lactam oligomer in the extraction of nylon-6. DE-A-43 24616 therefore proposes adding caprolactam monomer to the water at thestart of the extraction.

Processes are also known in which the extractables content is lowered byvaporizing the monomer and oligomer out of the polymer. DE-A-29 48 865discloses a demonomerization process wherein the polymer is subjected toa vacuum in the molten state and in the form of thin films.

All the processes mentioned have the disadvantage of requiring in someinstances multistage, costly and energy-intensive steps to demonomerizethe polymer and to work up the aqueous extract.

A further problem is the change in the product properties on furtherprocessing extracted nylon-6 having a low residual extractables contentand a defined viscosity. The polymer is usually processed, for examplefor extrusion or spinning, by reheating and liquefying it. The hightemperatures are known to change or increase the viscosity and theresidual extractables and residual monomer content. This viscosityinstability and remonomerization have an adverse effect not only onprocessing operations but also on product quality.

It is an object of the present invention to provide a process forproducing polyamides which have a reduced extractables and dimer contenteven in the unextracted state, so that the technical and economic effortneeded to extract the low molecular weight constituents and to work upthe aqueous extract is reduced, and which, under customary processingtemperatures and conditions, have a higher viscosity stability and alower increase in the residual extractables content than knownpolyamides.

We have found that this object is achieved according to the invention bya process for producing low-monomer and -oligomer nylon-6 by continuoushydrolytic poly-merization of aminonitriles, preferablyω-aminocapronitrile, ACN in short, and optionally furtherpolyamide-forming monomers in the presence of metal oxides. The metaloxides are used in a form which permits mechanical removal from thereaction mixture.

The novel continuous process for producing polyamides by reacting atleast one aminonitrile with water comprises the following steps:

(1) reacting at least one aminonitrile with water at a temperature offrom 200 to 290° C. at a pressure of from 40 to 70 bar in a flow tubecontaining a Brönsted acid catalyst selected from a beta-zeolite,sheet-silicate or metal oxide catalyst in the form of a fixed bed,

(2) diabatically or adiabatically expanding the reaction mixture fromstep (1) into a first separation zone to a pressure of from 20 to 40bar, the pressure being at least 10 bar lower than the pressure in step(1), and to a temperature within the range from 220 to 290° C. by flashevaporation and removal of ammonia, water and any aminonitrile monomerand oligomer,

(3) further reacting the reaction mixture from step (2) in the presenceof water at a temperature of from 200 to 290° C. and a pressure of from25 to 55 bar and in the presence or absence of a Brönsted acid catalystselected from a beta-zeolite, sheet-silicate or metal oxide catalyst inthe form of a fixed bed,

(4) diabatically or adiabatically expanding the reaction mixture fromstep (3) into a second separation zone to a pressure of from 0.01 to 20bar, the pressure being at least 20 bar lower than the pressure in step(3), and to a temperature within the range from 220 to 290° C. by flashevaporation and removal of ammonia, water and any aminonitrile monomerand oligomer.

The process preferably further includes the following step:

(5) postcondensing the product mixture from step (4) at a temperature offrom 230 to 280° C. and a pressure of from 0.01 to 10 bar.

The aminonitrile monomers and oligomers removed by flash evaporation insteps (2) and (4) are preferably returned into the reaction.

According to the invention, the heterogeneous catalysts used can beknown metal oxides, such as zirconium oxide, aluminum oxide, magnesiumoxide, cerium oxide, lanthanum oxide and preferably titanium dioxide aswell as silicates, such as beta-zeolites and sheet-silicates. Particularpreference is given to titanium dioxide in the anatase form. The anatasefraction is preferably at least 70% by weight, particularly preferablyat least 90%, especially essentially 100%. It was further found thateven silica gel, zeolites and doped metal oxides, doped with ruthenium,copper or fluoride, for example, distinctly improve the reaction of thereagents mentioned. Suitable catalysts are particularly notable for thefact that they are slightly Brönsted acidic and have a large specificsurface area. According to the invention, the heterogeneous catalyst hasa macroscopic form which permits mechanical separation of the polymermelt from the catalyst, for example by means of sieves or filters. Theproposal is for the catalyst to be used in extrudate chip form or ascoating on packing elements.

The individual process steps will now be more particularly described.

Step (1): Reaction of the reaction mixture in a flow tube which isfitted out with metal oxide catalysts and which is preferably operatedas a single liquid phase, at a temperature of from 200 to 290° C.,preferably from 210 to 260° C., particularly preferably from 225 to 235°C. The pressure is preferably set to within the range from 20 to 100bar, especially from 40 to 70 bar. The catalyst material is present as afixed bed and remains in the reactor.

Step (2): The pressurized reaction mixture is subsequently expandedadiabatically into a separation zone. The pressure in this separationzone is generally within the range from 20 to 40 bar, preferably withinthe range from 25 to 35 bar. The residence time in this first separationzone is generally within the range from 0.5 to 5 hours, preferably from2 to 4 hours, while the temperature should be within the range from 220to 290° C., preferably from 240 to 270° C. The process of expansion isaccompanied by a flash evaporation (utilizing the heat stored in thereaction mixture) of ammonia and water quantities still present in thereaction mixture. They contain volatile constituents such asaminocapronitrile monomer and oligomer. Rectification via a column canbe used to remove the water and ammonia vapors from the system andreturn the organics into the process, preferably into step 1.

Step (3): The pressurized mixture is subsequently transferred via a heatexchanger, together with added, likewise preheated water, into a furtherreactor, where it is further reacted at temperatures of from 200 to 290°C., preferably from 210 to 260° C., particularly preferably from 225 to235° C. The pressure in the reactor is preferably again set so that thereaction mixture is present as a single liquid phase. The pressure isgenerally within the range from 25 to 55 bar, preferably within therange from 30 to 45 bar. If desired, this stage likewise contains theaforementioned heterogeneous metal oxide catalysts, which are separatedin the form of a fixed bed from the product stream and remain in thereactor of the third stage.

Step (4): The pressurized reaction mixture is subsequently expandedadiabatically into a second separation zone. The pressure in thisseparation zone is generally within the range from 0.01 to 20 bar,preferably within the range from 0.1 to 10 bar, while the temperature iswithin the range from 220 to 280° C., preferably from 230 to 250° C. Theresidence time here is generally within the range from 0.5 to 10 hours,preferably from 2 to 8 hours. The process of expansion is accompanied bya flash evaporation whereby a portion of the ammonia and waterquantities present in the reaction mixture are liberated utilizing theheat of the reaction mixture. They contain volatile constituents such asaminocapronitrile monomer and oligomer. Rectification via a column canbe used to remove the water and ammonia vapors from the system andreturn the organics into the process, preferably into step 1.

Step (5): The reaction mixture is then preferably transferred into apostreaction zone, where the product mixture is postcondensed at atemperature of from 220 to 280° C., preferably from 240 to 250° C.

This process of reheating the reaction mixture followed by a flashevaporation can be repeated, if necessary. The amount of waterevaporated in the various separation zones and the associated loweringin the temperature can be specifically controlled through the particularpressure established. The advantage is that, owing to this adiabaticseparation or vaporization from the reaction mixture, no oligomers oradditives can separate out on apparatus and heat exchanger surfaces,thus preventing fouling by volatile organic and inorganic components.

In another preferred embodiment, the expanding reaction mixture hasenergy supplied to it through heat exchangers. The removal of the gasphase may be effected by using stirred or unstirred separating tanks ortank batteries and also by the use of evaporator apparatuses, forexample by means of circulatory evaporators or thin-film evaporators,filmtruders or by annular disk reactors, which ensure an enlarged phaseinterface. Recirculation of the reaction mixture or the use of a loopreactor may be necessary to enlarge the phase interface. Furthermore,the removal of the gas phase can be furthered by the addition of watervapor or inert gas into the liquid phase.

As customary additives and fillers there may be used pigments, such astitanium dioxide, silicon dioxide or talc, chain regulators, such asaliphatic and aromatic carboxylic and dicarboxylic acids, such aspropionic acid or terephthalic acid, stabilizers, such as copper(I)halides and alkali metal halides, nucleating agents, such as magnesiumsilicate or boron nitride, further, homogeneous catalysts, such asphosphorous acid, and also antioxidants in amounts within the range from0 to 5% by weight, preferably from 0.05 to 1% by weight, based on thetotal amount of monomers. Further suitable additives and comonomers aredescribed in DE-A-197 09 390. The additives are generally added prior tothe pelletizing and before, during or after, preferably after, thepolymerization. It is particularly preferable to add the additives tothe reaction mixture only after it has passed through the reaction zoneswhich contain the heterogeneous catalysts.

In a particularly preferred embodiment, chain regulators and otheradditives are added after the second reaction stage (separation zone)and before or in the third reaction stage. This has the advantage thatthe chain regulators can be dissolved directly in the water which iscontinuously fed into the third reaction stage.

The polymer obtained according to the invention can then be furtherprocessed according to. customary methods, for example converted intopiece form in a conventional manner by melt-extruding it in the form ofprofiles, which are quenched in a waterbath and then pelletized. Thepellets can then be conventionally extracted and subsequently orsimultaneously converted into high molecular weight polyamide. Theextraction can be effected for example with water or aqueous caprolactamsolution. Another possibility is gas phase extraction as described forexample in EP-A-0 284 968. The desired viscosity number for the endproduct is generally within the range from 120 to 350 ml/g. It can beset in a conventional manner.

The invention also provides for the use of metal oxides as heterogeneouscatalysts in a process for producing polyamides by reaction ofaminonitriles and water by using the metal oxides in a form whichpermits mechanical removal from the reaction mixture and removing themfrom the reaction mixture during or after the reaction, to reduce thelevel of extractables, to increase the viscosity stability and to lowerthe remonomerization rate in the polyamide obtained.

The metal oxide catalysts are preferably used in the form of granules,extrudates, fixed beds or catalyst-coated packing elements or internals.

The process of the invention is more particularly described by theexamples hereinbelow. Unless otherwise stated, all quantities andpercentages in the description and the claims are by weight. Theaminocapronitrile used has a purity of 99.9% by weight and contains 250ppm of tetrahydroazepine.

EXAMPLE 1

A reaction solution of aminocapronitrile and water (molar mixing ratioACN/water=1:6) is pumped to a heated heat exchanger and heated to thedesired reaction temperature within a few minutes. The pressure side ofthe feed pump is set to about 50 bar to ensure that the reaction systemforms a single phase. The heated reaction mixture is subsequently pumpedthrough a heated cylindrical tube having an internal diameter of 36 mmand a length of 1000 mm. The tube is packed with catalyst pelletsprepared from titanium dioxide from Finnti, type S150, and having adiameter of 4 mm and a length within the range from 5 to 20 mm. Thetitanium dioxide, which has a specific surface area of about 100 m²/g,is present in the anatase form and is held by sieves in the reactiontube and separated from the exiting product stream. For flashevaporation, the reaction mixture, which is under a pressure of about 50bar, is continuously expanded, at the end of the tube, via a controlvalve into a heated cylindrical separation vessel and to a pressure offrom 30 to 35 bar (see table). The reaction mixture forms two phases inthe process, so that the water and ammonia quantities present in themixture can pass into the gas phase. After a 3 h residence in theseparation vessel, which also serves as postreaction zone, the polymeris continuously pumped, by a melt pump, from the base region of thepostreactor into a second heated cylindrical tube having an internaldiameter of 36 mm and a length of 1000 mm, at a pressure within therange from 30 to 45 bar (see table). The tube is likewise packed withthe abovementioned catalyst pellets. The second flash evaporation iseffected by expanding the reaction mixture via a control valve into asecond cylindrical receiving vessel and pressures of from 1 to 2 bar.The separation vessel is also the location for the postreaction andespecially the postcondensation of the reaction solution, so that, aftera residence time of from 4 to 7 hours, the polymer obtained may becontinuously discharged by a melt pump from the base region of thereactor via a die into a waterbath in the form of profiles, consolidatedin the waterbath and pelletized.

The process parameters are listed in Table 1. The results show that thecorresponding polyamides have a low extractables content within therange from 9.0 to 9.8% by weight. The fraction of low molecular weightconstituents in the polyamides produced according to the invention isdistinctly lower than in polyamides obtained from caprolactam byconventional melt polymerization in a VK tube, described in DE-A-14 95198, EP-A-0 462 476 and EP-A-0 020 946. These have an extractablescontent of about 11% by weight.

EXAMPLE 2

A reaction solution of aminocapronitrile and water (molar mixing ratioACN/water=1:6) is pumped to a heated heat exchanger and heated to thedesired reaction temperature within a few minutes. The pressure side ofthe feed pump is set to about 50 bar to ensure that the reaction systemforms a single phase. The heated reaction mixture is subsequently pumpedthrough a heated cylindrical tube having an internal diameter of 36 mmand a length of 1000 mm. The tube is packed with catalyst pelletsprepared from titanium dioxide from Finnti, type S150, and having adiameter of 4 mm and a length within the range from 5 to 20 mm. Thetitanium dioxide, which has a specific surface area of about 100 m²/g,is present in the anatase form and is held by sieves in the reactiontube and separated from the exiting product stream. For flashevaporation, the reaction mixture, which is under a pressure of about 50bar, is continuously expanded, at the end of the tube, via a controlvalve into a heated cylindrical separation vessel and to a pressure offrom 30 to 40 bar (see also Table 2). The reaction mixture forms twophases in the process, so that the water and ammonia quantities presentin the mixture can pass into the gas phase. After a 3 h residence in theseparation vessel, which also serves as postreaction zone, the polymeris continuously pumped, by a melt pump, from the base region of thepostreactor into a second heated cylindrical tube having an internaldiameter of 36 mm and a length of 1000 mm, at a pressure within therange from 30 to 45 bar (see table). The tube is packed with Raschigrings (diameter 6 mm, length 6 mm). As well as the product stream fromthe separation vessel, a preheated aqueous solution, which in someprocess designs contains chain regulators such as adipic acid andtriacetonediamine, is pumped into the second tube reactor.

The second flash evaporation is effected by expanding the reactionmixture via a control valve into a second cylindrical receiving vesselto a pressure of 3 bar. After a residence time of 4 hours the reactionmixture is expanded by means of a further melt pump through a controlvalve into a third separator under a pressure between the pressure sideof the pump and the control valve sufficiently high for the mixtureagain to form a single liquid phase. The last separation vessel is alsothe location, at a pressure of 1.2 bar, for the postreaction andespecially the postcondensation of the reaction solution, so that, aftera residence time of 3 hours, the polymer obtained can be continuouslydischarged by a melt pump from the base region of the reactor via a dieinto a waterbath in the form of profiles, consolidated in the waterbathand pelletized.

The process parameters are listed in Table 2. The results show that thecorresponding polyamides have a low extractables content. The fractionof low molecular weight constituents in the polyamides producedaccording to the invention is again distinctly lower than in polyamidesobtained from caprolactam by conventional melt polymerization in a VKtube.

TABLE 1 Stage 2 Stage 4 Stage 1 Flash evaporation/ Stage 3 Flashevaporation/ Tubular reactor separator Tubular reactor separatorProduct* Run VWD T Pressure VWD T Pressure T VDW Pressure VWD T PressureExtractables No. [h] [° C.] [bar] [h] [° C.] [bar] [° C.] [h] [bar] [h][° C.] [bar] RV [%] 1 2 230 50 3 260 30 230 4 34 7 240 0.7 1.88 9.50 2 2230 50 3 260 30 230 4 34 4 240 0.7 1.87 9.37 3 2 230 50 3 260 30 230 434 4 240 0.3 1.86 9.36 4 2 220 50 3 260 30 230 4 34 7 240 0.3 2.00 9.105 2 240 50 3 260 30 230 4 34 7 240 0.3 1.89 9.06 6 2 250 50 3 260 30 2304 34 7 240 0.3 1.88 9.30 7 2 260 54 3 260 30 230 4 34 7 240 0.3 1.829.27 8 2 220 50 3 253 35 227 4 39 7 241 0.3 1.92 9.87 9 2 220 50 3 25330 227 4 34 7 242 0.3 1.72 9.60 10 2 260 55 3 260 35 230 4 39 7 240 0.31.72 9.83 VWD: residence time T: temperature RV: relative viscosity*after extraction and drying Pressure: overpressure

TABLE 2 Stage 3 Stage 2 Tubular reactor Stage 4 Stage 1 Flashevaporation/ H₂O/ Flash evaporation/ Product*** Tubular reactorseparator regu- Pres- separator Stage 5 Extrac- Run VWD T Pressure VWD TPressure lator VWD T sure VWD T Pressure VWD T Pressure ables No. [h] [°C.] [bar] [h] [° C.] [bar] add** [h] [° C.] [bar] [h] [° C.] [bar] [h][° C.] [bar] RV [%] 11 1 240 50 3 263 35 1 2 230 40 4 240 3.0 3 250 0.152.00 9.90 12 1 240 50 3 263 35 2 2 223 40 4 240 3.0 3 250 0.15 1.9810.27 13 1 240 50 3 263 35 2 2 230 40 4 240 3.0 3 250 0.15 1.99 9.93 141 240 50 3 263 35 2 2 240 40 4 240 3.0 3 250 0.15 1.94 10.13 15 1 240 503 263 35 2 2 250 40 4 240 3.0 3 250 0.15 1.95 10.07 16 1 240 50 3 263 352 2 250 35 4 240 3.0 3 250 0.15 1.97 9.50 RV: relative viscosity T:temperature VWD: residence time **1:5% of water + 0.29% oftriacetonediamine  2:5% of water + 0.29% of triacetonediamine + 0.3% ofadipic acid ***after extraction and drying Pressure: overpressure

Viscosity Stability of Exemplary Products

The viscosity stability is a measure of the spontaneous molecular weightbuildup of the polymer in the liquid and solid phase. The greater thestability, the smaller the change in the product viscosity within afinite time interval for which the polymer is present in the moltenstate, for example for further processing. A high viscosity stability isextremely important and desirable for many applications, since itensures consistent product properties and minimizes the effect ofprocessing operations on the viscosity.

The measured results hereinbelow show that the polyamides producedaccording to the invention have a higher viscosity stability thanconventionally polymerized comparative polyamides.

Measurement of Viscosity Stability

The products directly polymerized from ACN according to the inventionare extracted with water and dried under reduced pressure. The relativesolution viscosity (RV) is then determined in 1% strength by weightsolution in 96% strength by weight sulfuric acid at 25° C.

For comparison, caprolactam is conventionally hydrolyticallypolycondensed for a length of time such that the product viscositiescorrespond to the viscosities of the polyamides produced from ACN.

To be able to assess the viscosity stability, not only the solutionviscosities but also the melt viscosities of all productsamples—produced from ACN or from caprolactam—are redetermined followingaging for 15 and 25 minutes at 270° C. The melt viscosities aredetermined using a capillary rheometer at 270° C. and a shear gradientof 100/s.

TABLE 3 Measurements of viscosity stability Starting product After 15min After 25 min Residual aging at 270° C. aging at 270° C. moisture SV²SV² From run no. RV¹ [%] [dPas] RV¹ [dPas] RV¹ 9 1.74 0.029  40 1.84  601.84 Comparison 1 1.75 0.065 250 2.07 380 2.21 (caprolactam) 8 1.930.059 220 2.05 320 2.08 Comparison 2 1.93 0.046 420 2.21 550 2.30(caprolactam) 4 2.04 0.041 340 2.13 370 2.16 Comparison 3 2.05 0.039 6002.30 790 2.42 (caprolactam) ¹RV = relative viscosity (in solution); ²SV= melt viscosity

As the above table shows, the viscosity changes which the productsproduced from ACN undergo in the liquid (melt) phase are distinctlysmaller than those of the conventional polyamides from caprolactam.

Residual Extractables Content of an Exemplary Product

The extracted and dried chips of the exemplary product from run 4 aretempered in a tumble dryer in a nitrogen stream at 160° C. After atempering time of 24 hours, the polymer attains a relative viscosity of2.7.

To determine the residual extractables content, i.e., the extractablescontent of previously extracted samples, the chips are reextracted withmethanol. To this end, about 15 g of the polyamide sample areanalytically weighed into an extraction sleeve and Soxhlett-extractedwith 200 ml of methanol for 16 h. The methanol in the extract issubsequently distilled off at 50° C. and about 100 mbar in a rotaryevaporator, so that the residual extractables can be determinedgravimetrically. Care is taken to ensure that no monomer is lost in thecourse of the distillation of the methanol.

Remonomerization of an Exemplary Product

To measure the remonomerization rate, the change in the residualextractables content after 10 minutes' aging of the polymer in themolten state at temperatures of 240 and 270° C. is investigated. To thisend, the polyamide chips are melted in a viscometer (rheograph) at 240°C. or 270° C. for 10 min, and the residual extractables content of theproduct, extruded in filamentary form, is subsequently redeterminedusing the above method. The comparison in the extractables increase inthe polyamide produced from aminocapronitrile with the productsynthesized conventionally from caprolactam shows that the increase inthe residual extractables content and thus the remonomerization rate inthe polymer produced according to the invention is distinctly slower orless.

TABLE 4 Comparative example From run No. 4 Relative viscosity 2.7  2.7 Increase in extractables 0.76 0.49 at 240° C. (g/100 g) Increase inextractables 1.02 0.81 at 270° C. (g/100 g)

We claim:
 1. A continuous process for producing polyamides by reactingat least one aminonitrile with water, comprising the following steps:(1) reacting at least one aminonitrile with water at a temperature offrom 200 to 290° C. at a pressure of from 40 to 70 bar in a flow tubecontaining a Bronsted acid catalyst selected from a beta-zeolite,sheet-silicate or metal oxide catalyst in the form of a fixed bed, (2)diabatically or adiabatically expanding the reaction mixture from step(1) into a first separation zone to a pressure of from 20 to 40 bar, thepressure being at least 10 bar lower than the pressure in step (1), andto a temperature within the range from 220 to 290° C. by flashevaporation and removal of ammonia, water and any aminonitrile monomerand oligomer, (3) further reacting the reaction mixture from step (2) inthe presence of water at a temperature of from 200 to 290° C. and apressure of from 25 to 55 bar and in the presence or absence of aBrönsted acid catalyst selected from a beta-zeolite, sheet-silicate ormetal oxide catalyst in the form of a fixed bed, (4) diabatically oradiabatically expanding the reaction mixture from step (3) into a secondseparation zone to a pressure of from 0.01 to 20 bar, the pressure beingat least 20 bar lower than the pressure in step (3), and to atemperature within the range from 220 to 290° C. by flash evaporationand removal of ammonia, water and any aminonitrile monomer and oligomer.2. A process as claimed in claim 1, further comprising the followingstep: (5) postcondensing the product mixture from step (4) at atemperature of from 230 to 280° C. and a pressure of from 0.01 to 10bar.
 3. A process as claimed in claim 1, wherein the aminonitrilemonomers and oligomers removed by flash evaporation in steps (2) and (4)are returned into the reaction.
 4. A process as claimed in claim 1,wherein the reaction mixture in steps (1) and (3) is present as a singleliquid phase.
 5. A process as claimed in claim 1, wherein anaminonitrile used is aminocapronitrile.